We plan to continue with studies of the effects of feeding a low protein diet on hepatic amino acid transport. Since stimulation of alpha- aminoisobutyric acid (AIB) uptake by liver slices from rats force-fed casein hydrolysate is much less in protein-deprived than in normal animals, other stimulatory agents (gelatin hydrolysate, glycine and potassium chloride) will be tested to determine if they are more effective in protein-depleted rats than is casein hydrolysate. A comparison will be made of the relative efficacy of glucagon treatment of rats in the two groups. Cyclic AMP, when added to the incubation medium, also stimulates AIB transport significantly, its effects on liver slices from normal and protein-deprived rats will be compared. Studies of the competition among amino acids for entry into brain slices in vitro will also be continued and efforts will be made to reproduce effects observed in vivo through modification of the amino acid composition of the diet.